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Located 182 km west of Sydney in the Main Dividing Range, the Jenolan Caves have developed in the north and south sides of a natural archway in a belt of folded, near vertical limestone 7 km long. There have been very few scientific studies of the caves over the last 150 years, so the formation of the caves has been poorly understood and their minerals largely unknown.

the Devil's Coach House, Jenolan Caves
South-eastern entrance of the Devil's Coach House, Jenolan Caves. Image: Ross Pogson
© Australian Museum

In 1998, a joint research project between the Australian Museum, Sydney University and the Jenolan Caves Reserve Trust was begun to increase our understanding of the caves and their minerals. Jenolan minerals registered into the Australian Museum collection in 1898 and donated by Mr Voss Wiburd (the Jenolan Caves caretaker at that time) are being re-examined with modern methods of analysis. These minerals, such as clay, gypsum and phosphates, are being re-analysed with the latest methods of X-ray diffraction, X-ray chemical analysis, sulphur isotope studies and potassium-argon dating to extract new information on the formation of minerals at Jenolan. Previously, mineralogists would have used classical wet chemical analysis, determining composition from chemical tests on the dissolved mineral. Modern methods of analysis give more detailed data on the composition of minerals and give other chemical information, such as isotopic compositions, that were not available in the 1890s.

The 'Potatoes' in Lucas Cave, Jenolan
'The potatoes' in Jenolan caves. Image: Ross Pogson
© Australian Museum

As well as the old specimens, recently collected specimens are also being studied. For example, rounded knobbly formations in Lucas Cave viewed by tourists for over 140 years and known as 'The Potatoes' are not as they first appeared. They were always thought to be common calcite (calcium carbonate), but re-analysis has shown that they are an unusual calcium sulphate-phosphate mineral called ardealite. Ardealite has previously been found in Western Australia, but this is the first record of the mineral in New South Wales.

Modern analysis has also revealed another unusual feature in the Grand Archway and Devils Coach House. Sylvite (potassium chloride) and niter (potassium nitrate) are fragile water-soluble minerals which have formed from the interaction between geological and biological processes - that is, they have formed from the alteration of guano (dung) from the wombats and wallabies which frequented these large open caverns. The reaction of bat guano with limestone and clay has also produced some unusual phosphate minerals, such as crandallite, and the sulphate-phosphate mineral, ardealite.

So far, the joint study has identified eight mineral species not previously known from Jenolan, and the identities of six previously reported ones have been officially verified. The project is making many important discoveries which may lead to a re-evaluation of when and how the caves were formed. For example, research suggests some of the caves features were produced by water percolation upward from springs instead of downward seepage.